Error support

The db_strerror() function returns a pointer to the error
message corresponding to any Berkeley DB error return, similar to the ANSI C
strerror function, but is able to handle both system error returns and
Berkeley DB specific return values.

There are also two additional error methods, DB->err() and
DB->errx(). These methods work like the ANSI C X3.159-1989 (ANSI C) printf
function, taking a printf-style format string and argument list, and
writing a message constructed from the format string and arguments.

The DB->err() method appends the standard error string to the
constructed message; the DB->errx() method does not. These methods
provide simpler ways of displaying Berkeley DB error messages. For example,
if your application tracks session IDs in a variable called session_id,
it can include that information in its error messages:

Error messages can additionally be configured to always include a prefix
(for example, the program name) using the DB->set_errpfx() method.